In recent years, flat panel displays are used in various commodity products and fields, and thus flat panel displays are required to have a large size, high image quality and low power consumption.
Under the circumstances, organic EL display devices, which include an organic EL element that utilizes electro luminescence of an organic material, are attracting great attention as all-solid state flat panel displays that are excellent as having capability of low voltage operation, quick responsivity and light emission.
Active matrix type organic EL display devices, for example, are provided with a thin film-like organic EL element on a substrate having a TFT (thin film transistor). In the organic EL element, organic EL layers including a light emitting layer are laminated between a pair of electrodes. The TFT is connected to one of the pair of electrodes. Then, voltage is applied across the pair of electrodes so as to cause the light emitting layer to emit light, whereby an image is displayed.
In a full-color organic EL display device, generally, organic EL elements including light emitting layers of respective colors of red (R), green (G) and blue (B) are formed and arranged on a substrate as sub-pixels. By causing these organic EL elements to selectively emit light at the desired brightness by using the TFT, a color image is displayed.
In order to manufacture an organic EL display device, it is necessary to form a light emitting layer made of organic light emitting materials that emit respective colors in a predetermined pattern for each organic EL element.
Known methods for forming light emitting layers in a predetermined pattern are vacuum vapor deposition method, inkjet method and laser transfer method. For example, the vacuum vapor deposition method is often used for low molecular organic EL display devices (OLEDs).
In the vacuum vapor deposition method, a mask (also called a “shadow mask”) having a predetermined pattern of openings is used. The deposition surface of a substrate having the mask closely fixed thereto is disposed so as to oppose a vapor deposition source. Then, vapor deposition particles (film forming material) from the vapor deposition source are deposited onto the deposition surface through the openings of the mask, whereby a predetermined pattern of a coating film is formed. Vapor deposition is performed for each color of the light emitting layer, which is referred to as “vapor deposition by color”.
For example, Patent Documents 1 and 2 describe a method for performing vapor deposition by color in which light emitting layers for respective colors are formed by sequentially moving a mask with respect to a substrate. With such a method, a mask having a size equal to that of a substrate is used, and the mask is fixed so as to cover the deposition surface of the substrate at the time of vapor deposition.
With conventional methods for performing vapor deposition by color as described above, as the substrate becomes larger, the mask needs to be large accordingly. However, when the mask is made large, a gap is likely to appear between the substrate and the mask by the mask being bent or being extended by its own weight. In addition, the size of the gap varies depending on the position of the deposition surface of the substrate. For this reason, it is difficult to perform highly accurate patterning, and it is therefore difficult to achieve high definition due to the occurrence of vapor deposition positions being positionally offset and the occurrence of color mixing.
Also, when the mask is made large, the mask as well as a frame or the like for holding the mask need to be gigantic, which increases the weight and makes handling thereof difficult. As a result, there is a possibility that productivity and safety might be compromised. Also, the vapor deposition device and devices that are used together therewith need to be made gigantic and complex as well, which makes device designing difficult and increases the installation cost.
For the reasons described above, the conventional methods for vapor deposition by color that are described in Patent Documents 1 and 2 are difficult to adapt to large-sized substrates, and it is difficult to perform vapor deposition by color on large-sized substrates such as those having a size exceeding 60 inches on a mass manufacturing level.
Patent Document 3 describes a vapor deposition method for causing vapor deposition particles discharged from a vapor deposition source to adhere to a substrate after causing the vapor deposition particles to pass through a mask opening of a vapor deposition mask while relatively moving the vapor deposition source and the vapor deposition mask with respect to the substrate. With this vapor deposition method, even in the case of large-sized substrates, it is not necessary to increase the size of the vapor deposition mask in accordance with the size of the substrates.
However, because it is necessary to relatively move the vapor deposition mask with respect to the substrate, the substrate and the vapor deposition mask need to be spaced apart from each other. With Patent Document 3, vapor deposition particles that fly from various directions may enter the mask openings of the vapor deposition mask, and therefore the width of the coating film formed on the substrate is wider than the width of the mask opening, resulting in blurring at the edge of the coating film.
Patent Document 4 describes a vapor deposition device including a plurality of nozzles arranged along a first direction, a plurality of slits arranged along the first direction, and a plurality of shielding walls arranged along the first direction between the plurality of nozzles and the plurality of slits. Vapor deposition particles respectively discharged from the plurality of nozzles pass through spaces between the shielding walls and the plurality of slits, and adhere to the substrate traveling in a second direction that is orthogonal to the first direction so as to form a thin film. According to this vapor deposition device, the shielding walls limit the incidence angles of the vapor deposition particles in the first direction entering the slits, and therefore blurring at the edges of a coating film in the first direction formed on the substrate can be reduced.